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Causes of rolling, wilted tomato leaves

Posted: Jun. 24, 2018 12:01 am

Don't get me wrong. I love a fresh summer tomato, straight off the vine and onto my ham sandwich. But often there are times during the growing season where I wonder if that tomato goodness is worth the effort.

Let's face it; tomatoes are a lot of work.

Despite the amount of work, tomatoes are a labor of love and a mainstay in most gardens. However, I would contend there is an unwritten rule that "where there are tomatoes, there will be tomato problems."

So far this growing season, the primary tomato question tossed my way has dealt with curling leaves. Multiple gardeners in West-Central Illinois have called describing or emailed me pictures of tomato plants whose leaf edges have rolled up and inward.

My first inclination is to suspect disease. While diseases such as soil-borne wilts or bacterial infections produce similar leaf roll or wilting symptoms, these are often accompanied with obvious infection points on the aboveground growth or yellowing leaves. I am not seeing any of these disease symptoms in the submitted homeowner questions. Instead, what is pictured are perfectly green leaves that are rolled up like a burrito.

My next route of investigation is to look very carefully at the leaves. Are they twisted and malformed? Is the garden near a lawn or agriculture field that was sprayed with a broadleaf herbicide? That may indicate herbicide damage. Tomatoes are quite susceptible to herbicides, especially plant growth regulator herbicides, which have the unfortunate ability to volatilize (vaporize) and drift to non-target plants when sprayed during hot and dry weather.

While that may account for a few homeowners, most of what I'm seeing is not due to herbicide damage. In fact, what is actually happening is a natural defense of the tomato plant. During very hot and dry weather, tomato leaves will curl and sometimes wilt to reduce water loss. This reaction is known as physiological leaf roll.

Most of the time the tomato plants will recover from mild cases of physiological leaf roll, with little impact to yield. However, prolonged exposure to hot, dry weather can cause severe leaf roll from which the plant may not recover.

The bad news -- summer just started, and we're bound to encounter more hot weather. The good news -- there are things you can do to reduce heat stress on your tomatoes.

º Avoid severe pruning. Tomato leaves work together to shade and keep the plant cool. By removing too much leaf cover at one time, the plant is more exposed and prone to heat stress.

º Try to keep temperatures below 95 degrees Fahrenheit. You may ask "tomatoes are a summer crop, right?" Well, yes, but they are also native to alpine regions in Central and South America. Tomatoes don't perform well during the hottest times of our Midwestern growing season. Use shade cloth or a misting system to keep the tomatoes cooler during the hottest parts of the day.